1. Field of the Invention
The present invention relates generally to fabrication of fine patterns for use in fabricating patterns for a semiconductor device and inspection method therefor, and more particularly to fabrication of fine patterns by selective surface reaction and inspection method therefor.
2. Description of the Background Art
In recent years, with miniaturization of semiconductor devices, resist pattern fabricating process by using selective surface reaction and development by dry etching has been developed as a method of fabricating a fine resist pattern having pattern width on the order of submicron. This resist pattern fabricating process is expected as a resist pattern fabricating process of the next generation because of the following advantages as compared with a conventional fine pattern fabricating method using resist and developer.
As a representative of such resist pattern fabricating process as described above, DESIRE (Diffusion Enhanced Silylating Resist) process is reported in "DESIRE: a novel dry developed resist system" by Coopmans and B. Roland, SPIE Proc., 631,34 (1986).
(i) The depth-of-focus is increased under the ultraviolet light exposure, resulting in susceptibility to the effect of an underlying substrate on which a resist pattern is formed.
(ii) Under for ultra-violet light exposure such as excimer laser, deterioration of a pattern shape can be prevented resulted from the fact that energy absorption of a resist is so large that the exposure can not be done to a bottom portion of the resist.
(iii) Under electron beam exposure, blur of a pattern due to dispersion of the electron beam in the resist can be eliminated.
A description will be given of a case in which the DESIRE process is applied to pattern transfer by the ultra-violet light exposure. FIGS. 9A through 9E are partially sectional views showing sequential steps of a method of fabricating a pattern in case the DESIRE process is applied in fabricating a fine pattern by the ultraviolet exposure.
Referring to FIG. 9A a predetermined film 12 is formed over a silicon substrate 11. A resist 13 for dry development is spin-coated over the film 12. As a resist for dry development, PLASMASK resist, a product of Japan Synthetic Rubber, for example. Dry development is a method of developing a resist by using oxygen plasma and the like while ordinarily it is developed by using organic solvent and alkaline solution. The resist for dry development is a special resist formed of a material suitable for the above-described dry development. The resist 13 for dry development is selectively irradiated by ultra-violet light 15 of a wavelength of 436 nm or 360 nm through a mask 14. As the foregoing, as a result of the formation of a portion 131 exposed to the ultra-violet light in the resist 13 as shown in FIG. 93, a pattern of the predetermined mask 14 is transferred onto the resist.
Referring to FIG. 9C, a silylated portion 132 is formed on a surface of the portion 131 exposed to the ultra-violet light by the silylation treatment. The silylation treatment is carried out by introducing the substrate maintained at the temperature of 100.degree.-180.degree. C. into nitrogen carrier gas atmosphere containing hexamethyldisilazane (HMDS). The hexamethyldisilazane is referred to as silylating reagent. The hexamethyldisilazane selectively diffuses in the portion 131 exposed to the ultra-violet ray to cause silylation. Schematically, the silylation is carried out as the following.
In the portion 131 exposed to the ultra-violet light in the resist, quinondiazides contained as a photosensitive material in the resist changes into indene carboxylic acid. Therefore, under the heating at the above-described temperature, crosslinking reaction of the novolak resin included in the resist occurs more remarkably in the non-exposed portion than in the exposed portion 131. As a result, the HMDS as the silylating reagent easily enters the portion 131 exposed to the ultra-violet light, so that silylation reaction between the novolak resin and the HMDS occurs, that is, molecules including silicon atoms enters the surface portion of the portion 131 exposed to the ultra-violet light, thereby forming the silylated portion 132. The silylation treatment is described in detail in "THE PATTERN FABLICATION BY SILILATION (SILYLATION) PROCESS" PP. 69-73 by S. Ito et al, 1988 Dry Process Symposium .
As shown in FIG. 9D, the silylated portion 132 changes into a silicon oxide film 133 by the introduction of the substrate into anisotropic oxygen plasma. Then, as shown in FIG. 9E, only the non-exposed portion is selectively removed in the anisotropic oxygen plasma to be dry developed. As the foregoing, the selective removal of the resist is carried out by using the selectively silylated portion in the surface portion of the resist as a mask. As a result, a fine pattern formed of a negative type resist is obtained.
FIGS. 10A through 10D are partially sectional views showing sequential steps of fabricating a resist pattern when the above-described DESIRE process is applied to a resist pattern fabricating process by the electron beam exposure. The resist pattern fabricating process is reported in "PRIME; New Dry Developed Positive Working System for E-beam and Deep U.V. Lithography" by C. Pierrat et al., at 3-Beam Conference (June, 1989) in Montery (U.S.A.)
Referring to FIG. 10A, a resist 23 for dry development is spin-coated over a substrate 21. A predetermined pattern is drawn on the resist 23 for dry development by electron beams 25. Referring to FIG. 10B, a portion 231 exposed to the electron beams is formed in the resist 23 for dry development. Thereafter, the entire resist 23 is irradiated with ultra-violet light 26. As a result, the portion 231 exposed to the electron beams is crosslinked by the electron beams and a portion nonexposed to the electron beams which is exposed only to the ultra-violet light in the resist 23 changes into a substance hard to be crosslinked.
Thereafter, as shown in FIG. 10C, in the silylation process, the silylating reagent, that is, the molecules containing silicon atoms penetrates the non-exposed portion. As a result, a silylated portion 232 is formed on the surface of the non-exposed portion (the portion irradiated only with the ultra-violet rays). Referring to FIG. 10D, for example, by the reactive ion etching process in the anisotropic oxygen plasma, a portion of the resist to which no silicon atom penetrates, that is, the exposed portion 231 is selectively removed. As the foregoing, as a result of the selective etching of only the portion irradiated with the electron beams, a positive type fine resist pattern is fabricated.
In fabricating a pattern for a semiconductor device, normally another pattern is registered with respect to one pattern formed on an underlying substrate. The registration is carried out by detecting an alignment mark formed on the underlying substrate in scanning predetermined energy beam such as laser beam and electron beam.
However, in a such case where the detection is not properly performed in scanning the alignment mark, the upper layer pattern becomes out of register with the underlying substrate. If the succeeding steps are sequentially carried out with the resist pattern out of register to manufacture a semiconductor device, the manufactured semiconductor device is not capable of operating normally. In order to avoid this, the registration accuracy is checked at the stage of the formation of the resist pattern by using a device for measuring minute dimensions, for example, LAMU-600. In checking the registration accuracy, if it is detected that the pattern is out of register, it is necessary to remove the fabricated resist pattern and apply an additional register on the substrate to newly form a pattern.
In case of a resist pattern fabricated by using conventional resist and developer, since the resist is formed of an organic substance containing carbon, oxygen and hydrogen as main components, it is easily removed through the exposure to the oxygen plasma atmosphere. However, in the case of the resist pattern fabricated by the DESIRE process as described above, since the silicon atoms diffuse on the surface of the resist left a the pattern, the resist can not be easily removed just by exposing the resist pattern to the oxygen plasma atmosphere. This is because while the main components, carbon, oxygen and hydrogen constituting the resist are easily oxidized and evaporated in the oxygen plasma, the silicon atoms are caked as oxide by the oxidation. Then, in order to remove the silicon atoms contained in the resist, the resist pattern needs to be exposed in plasma atmosphere having fluorine atoms such as CF.sub.4.
However, if the exposed surface of the underlying substrate of the resist pattern is exposed in the plasma atmosphere having the fluorine atoms in order to remove the resist, the elements of the semiconductor device containing a lot of silicon atoms such as silicon and silicon oxide (SiO.sub.2) formed on the underlying substrate are damaged. Therefore, in case the resist pattern fabricated by using the above-described DESIRE process is out of register, it is difficult to remove the resist by using the plasma.